/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using Checksum = SupportClass.Checksum;
using CRC32 = SupportClass.CRC32;

namespace Lucene.Net.Store
{

    /** Writes bytes through to a primary IndexOutput, computing
     *  checksum.  Note that you cannot use seek().*/
    public class ChecksumIndexOutput : IndexOutput
    {
        IndexOutput main;
        Checksum digest;

        public ChecksumIndexOutput(IndexOutput main)
        {
            this.main = main;
            digest = new CRC32();
        }

        public override void WriteByte(byte b)
        {
            digest.update(b);
            main.WriteByte(b);
        }

        public override void WriteBytes(byte[] b, int offset, int length)
        {
            digest.update(b, offset, length);
            main.WriteBytes(b, offset, length);
        }

        public long GetChecksum()
        {
            return digest.getValue();
        }

        public override void Flush()
        {
            main.Flush();
        }

        public override void Close()
        {
            main.Close();
        }

        public override long GetFilePointer()
        {
            return main.GetFilePointer();
        }

        public override void Seek(long pos)
        {
            throw new System.SystemException("not allowed");
        }

        /**
         * Starts but does not complete the commit of this file (=
         * writing of the final checksum at the end).  After this
         * is called must call {@link #finishCommit} and the
         * {@link #close} to complete the commit.
         */
        public void PrepareCommit()
        {
            long checksum = GetChecksum();
            // Intentionally write a mismatched checksum.  This is
            // because we want to 1) test, as best we can, that we
            // are able to write a long to the file, but 2) not
            // actually "commit" the file yet.  This (prepare
            // commit) is phase 1 of a two-phase commit.
            long pos = main.GetFilePointer();
            main.WriteLong(checksum - 1);
            main.Flush();
            main.Seek(pos);
        }

        /** See {@link #prepareCommit} */
        public void FinishCommit()
        {
            main.WriteLong(GetChecksum());
        }

        public override long Length()
        {
            return main.Length();
        }
    }
}
